Fibromyalgia, also known as fibromyalgia/fibromyalgic syndrome (FMS), fibromyositis, polyinsertionitis, polyenthesopathy, myofibrositis, myofascitis, ‘tension’ rheumatism, ‘psychogenic’ muscular rheumatism, diffuse idiopathic pain syndrome (DIPS) or fibrositis, is a debilitating syndrome characterised by widespread chronic body pain and often with other symptoms such as fatigue, sleep disturbance, reduction in slow wave sleep, sensitivity to touch and light and cognitive problems. The National Fibromyalgia Association indicates that the syndrome affects ˜3-6% of the world population. Current treatment includes pregabalin and it has been reported that gabapentin is effective in treating FMS symptoms (Arnold et al., (2007) Arthritis Rheum. 56(4):1336-44). The aetiology of the syndrome is still not yet fully understood and there is still an unmet need for an effective treatment with minimal side effects.
Eslicarbazepine acetate (ESL, S-(−)-10-acetoxy-10,11-dihydro-5H-dibenz/b,f/azepine-5-carboxamide; also known as BIA 2-093) is a new voltage-gated sodium channel (VGSC) blocker that shares with carbamazepine (CBZ) the dibenzazepine nucleus bearing the 5-carboxamide substituent, but is structurally different at the 10,11-position (see BENES, J., PARADA, A., FIGUEIREDO, A. A., ALVES, P. C., FREITAS, A. P., LEARMONTH, D. A., CUNHA, R. A., GARRETT, J. & SOARES-DA-SILVA, P, (1999), “Anticonvulsant and sodium channel-blocking properties of novel 10,11-dihydro-5H-dibenz[b,f]azepine-5-carboxamide derivatives,” J Med Chem, 42, 2582-2587).
This molecular variation results in differences in metabolism, namely by preventing the formation of toxic epoxide metabolites, such as carbamazepine-10,11 epoxide, and unnecessary production of enantiomers or diastereoisomers of metabolites and conjugates (see HAINZL, D., PARADA, A. & SOARES-DA-SILVA, P. (2001), “Metabolism of two new antiepileptic drugs and their principal metabolites S(+)- and R(−)-10,11-dihydro-10-hydroxy carbamazepine,” Epilepsy Res, 44, 197-206), without losing pharmacological activity (see the above Benes reference).